\(\sqrt{x+3}+\sqrt{1-x}=2-8\sqrt{\left(x+3\right)\left(x+1\right)}\)
\(\Leftrightarrow\sqrt{x+3}+\sqrt{1-x}-2+8\sqrt{\left(x+3\right)\left(x+1\right)}=0\)
\(\Leftrightarrow\sqrt{x+3}-\frac{x+3}{\sqrt{1-x}+2}+8\sqrt{\left(x+3\right)\left(x+1\right)}=0\)
\(\Leftrightarrow\sqrt{x+3}\left(1-\frac{\sqrt{x+3}}{\sqrt{1-x}+2}+8\sqrt{x+1}\right)=0\)
\(\Leftrightarrow\sqrt{x+3}=0\)
\(\Leftrightarrow x=-3\)